dirstatemap: remove `_insert_entry` This was needed as a compatibility layer for the Python and Rust implementations, but it is not called from anywhere in Rust anymore. The two remaining calls have been inlined. Differential Revision: https://phab.mercurial-scm.org/D12501

{
    "conduit_uri": "https://phab.mercurial-scm.org/api",
    "phabricator.uri": "https://phab.mercurial-scm.org/",
    "repository.callsign": "HG",
    "arc.land.onto.default": "@",
    "base": "hg:.^"
}